A door of an automobile is constituted by assembling an outer panel which creates an appearance and an inner panel which is a frame of the door and chiefly maintains a strength by, for example, hemming (180° bending). Door component parts such as a door lock mechanism, a door glass, and a window regulator are housed between the outer panel and the inner panel.
A recent automobile often has, between an outer panel and an inner panel, a door impact beam being a long reinforcing member which is disposed in a manner that both ends thereof are fixed in a front and rear direction of the automobile, for the purpose of improving safety at the time of side collision. The door impact beams are divided largely into a closed cross-section type whose material is, for example, a round pipe or the like, and an open cross-section type which has, for example, a groove-shaped transverse cross-section, and each type of the door impact beams absorbs impact energy by three-point bending deformation occurring at a collision load input position being a point of action when an impact load by side collision is applied.
As described above, since it is necessary that the door impact beam is disposed in a narrow space between the outer panel and the inner panel, avoiding interference with the aforementioned various door component parts, the door impact beam is required to absorb collision energy efficiently with a small cross-section. Various suggestions have been proposed regarding such door impact beams.
Patent Literature 1 discloses invention of a door impact beam made of a thin steel sheet with a hat-shaped open cross-sectional shape which has: a groove bottom portion; two edge line portions continuing to the groove bottom portion; two vertical wall portions continuing to the two edge line portions respectively; two curved portions continuing to the two vertical wall portions respectively; and two flanges continuing to the two curved portions respectively, wherein a reinforcing plate is disposed in a part of one of the vertical walls—one of the edge line portion—the groove bottom portion—the other edge line portion—a part of the other vertical wall, to thereby partially reinforce a range between a plane of the groove bottom portion and the edge line portions, so that cross-section collapse of the hat-shaped open cross-sectional shape is suppressed at the time of collision, whereby an absorption performance of collision energy is improved.
Patent Literature 2 discloses invention of a door impact beam made of a thin steel sheet with a practically U-shaped open cross-sectional shape, wherein formation of a bead projecting toward the inside at a top portion of a U-shape reduces a possibility of fracture while increasing an absorption performance of impact energy.
Incidentally, Patent Literature 3, which relates to a center pillar of an automobile, discloses invention of the center pillar which has a bending deformation promoting bead and an auxiliary bead provided in a top portion plane of a reinforcement disposed as a reinforcing member to an outer panel made of a resin.